Magnetic alloy



ALBERT A; FREY, or ronnsrr HILLS, wxLKrNsiauRG,

wtasrmenousn nnnc'rmc & 'MANUFACTURING Patented Feb. 16, 1932 i uNiTsn s TAT s PATENT OFFICE PENNSYLVANIA MAGNETIC ALLOY No Drawing.

M invention relates to alloys and more particularly to magnetic alloys containing iron, aluminum and arsenic.

The principal obj eet of my invention is to provide a ductile alloy containing iron, aluminum and arsenic that shall have a high electrical resistivity and a low core loss.

Another object of my invention is to provide an alloy containing iron, aluminum and arsenic which shall have higher ductility than ironwsilicon alloys and which, when utilized in cores for transformers, shall be characterized by having a total core loss as lowvas 1.0. when tested at an inducwatt per-kilogram, tioi of 10,000 gausses and cycles per secon A further object of my invention? is to provide a core. for electrical apparatus, such as transformers, generators and the like, comprising rolled and annealed laminations containing an alloy'of iron, aluminum 'and' arsenic;

Iron-silicon alloys have heretofoie been extensively employed as a core material in electrical apparatus, such as-transformers. When more than silicon, however, is utilized, an alloy produced of such materials becomes brittle and is diflicult to roll and punch. Consequently, the amount of silicon which may .be utilized is limited. It is essential, however, in producing magnetic materials that the material utilized shall have a high electrical resistance in order to reduce eddy current losses. Iron-aluminum alloys have also been utilized, to a certain extent, as aluminum is very effective in increasing the electrical resistance of iron, but, since the amount of this element which may be added to iron is limited because of the difliculties encountered in the melting operation, alloys comprisin desira le magnetic properties are diflicult to prepare by economical methods.

I have made the discovery that the electrical properties of iron-aluminum alloys may be considerably improved by the addition of .1% to 6% of arsenic and that an alloy so produced may be rolled and punched. When properly annealed, my improved alloy has a higher maximum permeability than iron-siliiron and aluminum having the most Application filed March 24, 1931. Serial No. 525,045.

con alloys and is'characterized by having an especially low core loss.

In practicing my invention, I melt iron'in a suitable metallurgical furnace, such as an electric induction furnace, which is maintained at a temperature of from 2700 F. to

2900 F. At this temperature, arsenic may be added to the molten iron, either as metallic arsenic or as ferro-arsenic or it may be introduced by passing a stream of arsenic vapor, arsene or arsenic hydride into the molten iron.

- After the arsenic has been dissolved in the molten iron, aluminum is added, either as pure aluminum or as a ferro-alloy of aluminum, or the arsenic and aluminum may be added to the molten iron in one operation. I prefer, however, to introduce the arsenic into the iron before adding the aluminum because I havefound that, if the arsenic is added first, any oxides that maybe present in the molten iron will react with the arsenic toform oxides of arsenic which volatilize at the temperatures prevailing and are eliminated, leaving very little oxygen to react PENNSY'LVANIA, ASSIGNOR TO COMPANY, A CORPORATION OF with the aluminum. When aluminum and shall first be carefully deoxidized by the addition of a small amount of a suitable deoxidizer, such as carbon, silicon, or calcium silieide.

The alloy, produced as above specified, may then be cast into ingots of any desired form to be subsequently rolled into bars or sheets, according to the usual rolling-mill practice.

a The amount of arsenic and aluminum which are added to the iron will depend upon the magnetic and mechanical characteristics I desired, and, as a rule, will vary between 1% to 6%, by Weight, of arsenic, and .1% to 12%, by weight, of aluminum.

The amount of arsenic employed will depend upon the saturation value, permeability, core loss and resistivity desired for the alloy and also upon the amount of aluminum which is utilized. If a high saturation value is required, a small amount, say not more than is suflicient. The function of the arsenic in the alloy, however, is to lower the melting point of the iron and increase its fluidity, thereby compensating for the effect of the aluminum which has a tendency to make the alloy in the molten state very viscous. If less .1%, by weight, of arsenic is employed, it will have no appreciable effect upon the melting point of the iron while, if more than 6% is utilized, sheets formed of the alloy can be rolled only with great difiiculty because the sheets adhere to each other during the hot-pack rolling operation.

I prefer to utilize from to 3%, by weight, of arsenic in order to produce an alloy having valuable magnetic properties. However, an alloy having high electrical resistivity and a low coreloss may be produced containing from .2% to 6%, by weight,

' of arsenic.

The amount of aluminum employed will, in general, depend upon the electrical resistivity desired. The brittleness and resistivity of the alloy increase with the aluminum content. I have found that less than .1%, by weight, of aluminum would have no appreciable eflect upon the physical and magnetic properties of the alloy while, if more than 12%, by weight, is utilized, the alloy will be so brittle that it will be practically unforgeable. Alloys containing from .1% to 6%, by weight, of aluminum have high resitivity and satisfactory physical properties. However, I prefer to utilize from 2% to 4%, by weight, of aluminum. An alloy containing the arsenic and aluminum within the amounts specified is ductile and non-porous, possess high fluidity in the molten state and may be readily cast.

After the alloy is cast and rolled, in the manner specified, it is then annealed for the purpose of improving the magneticproperties. A suitable annealing operation may consist in heating the rolled sheets to a temperature of 900 C. to 1400 C. in air, a neutral'atmosphere, or in hydrogen for a period of 1 to 48 hours and then cooling in the furnace. t

In preparing laminations for electrical ap paratus, such as transformers, however, I prefer to anneal the sheet material in air, a neu" tral atmosphere, or in hydrogen for a period of several days at a temperature of 900 C. to 1400 C. The material is cooled in the furnace, the laminations are punched andthe material is then re-annealed for a similar period at a temperature of 700 C. to 800 U.

My preferred alloy, when properly annealed, has exceptionally good-magnetic characteristics. For example, an alloy containingj2.19%, by wei ht, of aluminum, and 2.14%,by'we1ght, 0 arsenic, the balance being comparatively pure iron, in the form of a rolled sheet, had a core loss of approximately 1.0 watt per kilogram at an induction of 10,000 gausses and at cycles per second.

The physical and electrical characteris- Tensile strength 61,500 pounds per square inch. Elongation in 2" 23 Reduction of area 25.5%

Brinell hardness. 140

Resistivity 42 michroms per cm. Maximum permeability 26,100 at 3:7850 gausses H=.3 gilbert per cm. Core loss at B=10,000 1.0 to 1.25 watts per kilogram My improved magnetic alloys are superior to iron-silicon alloys because they have greater ductility and less brittleness. They also have a higher magnetic permeability,

higher resistivity and a lower core loss than iron-silicon alloys and, since they are not as hard as iron-silicon alloys, the punching operations are facilitated, which prolongs the life of the punching dies.

Furthermore, the arsenic'acts as a purifier, while the alloy is in the molten state, because it reacts witn oxides and non-metallic inclusions to form volatile compounds which may be eliminated. The aluminum is a vital constituent of my improved alloy because when sheets are formed fromiron-arsenic alloys alone, they have the tendency to adhere to each other when a plurality of them are rolled, as in the hot-pack rolling process.

While I have disclosed my invention in considerable detail and have-given specific examples, it will be understood that the examples are to be construedv as illustrative and not by Way of limitation. For example, it will be understood that the alloy will contain a small amount of impurities, such as carbon, silicon, sulphur or phosphorous or compounds thereof. It is preferred, however, that the amount of magnetically detrimental impurities shall be less than .02%. Electrolytic iron or a high-grade commercial iron, such as Armco iron may be utilized. Other elements or impurities may be present pro:

vided they are not magnetically detrimental,

Other modifications will become apparent to those skilled in the art without departing from the spirit and scope of my invention. It is, therefore, desired that only such limitations shall be imposed as are indicated in the appended claims.

' I claim as my invention:

1. A magnetic alloy comprising iron as a major constituent and aluminum and arsenic as minor constituents.

2. A magnetic alloy comprising iron as a major constituent and from .1% to 6%, by weight, of arsenic, and from .1% to 12%, by weight, of aluminum.

3 A magnetic alloy comprising iron as a ma or constituent and substantially equal amounts'of arsenic and aluminum.

4. A magnetic alloy comprising iron as, a

major constituent, said alloy having a combined arsenic and aluminum content of from 2% to 18%, by weight.

mamas 5. A magnetic ductile alloy comprising iron as a major constituent anal from .1% "to 6%, by weight, of aluminum, and from .5 to 4%, by weight, of arsenic.

6. A magnetic alloycomprising iron as a major constituent and from 2% to 4%, by weight,- of aluminum, and. from 25% to 3%, by weight, of arsenic,

7. A magnetic alloy comprising at least I by weight, of iron, and from 1% to 6%, by weight, of arsenic, and from .1%'to 12%, by weight, of aluminum, said alloy having a core loss of less than watts per kilogram at an induction of 10,000 gausses.

8. An article of manufacture comprising a rolled sheet of ma netic material composed of an alloy comprising at least 85% iron, .1% t0 6% arsenic, and .1% to 12% aluminum.

9. A lamination for electrical apparatus comprising a rolled sheet of magnetic material com osed of an alloy comprising at least 85% iron, .1% to 6% arsenic, and om .1% to 12% aluminum.

10. A transformer core having a plurality of laminations of magnetic sheet material, each of said sheets being formed of an alloy comprising at least 85% iron, .1% to 6% arsenic, and from .1% to 12% aluminum.

In testimony whereof, I have hereunto subscribed my name this 20th day of March,

ALBERT A. FREY. 

